Process for the stretching of polyamidic fibres



ROCESS FOR THE STRETCHING OF POLYAMIDIC FIBRES Filed July 15, 1964 May 7, 1968 |ER| ET AL 2 Sheets-Sheet 1 Birefringency Of The Non- Stretched Filomnt X I000 JNVENTORS Luis; Cal nnuall /11,

7 6th; Marvzzi and Ginny Niza'l'la- May 7, 1968 CICERI ET AL 3,382,307

PROCESS FOR THE STRETCHING OF POLYAMIDIC FIBRES Filed July 15, 1964 2 Sheets-Sheet 2 United States Patent 3,382,307 PROCESS FOR THE STRETCHING OF POLYAMIDIC FIBRES Luigi Ciceri, Como, Bruno DAlo, Palazzolo Milanese, and Pietro Moruzzi and Giuseppe Nicotra, Milan, Italy, assignors to Snia Viscosa Societa Nazionale Industria Applicazioni Viscosa S.p.A., Milan, Italy, 'a company of Italy Filed July 15, 1964, Ser. No. 382,754 Claims priority, application Italy, July 23, 1963, Patent 702,082 9 Claims. (Cl. 264210) ABSTRACT OF THE DISCLOSURE Polycapronarnide having an intrinsic viscosity from 1.25 to 1.48 is spun at a speed of 380 to 750 m./minute to obtain a spun polycapronamide having a birefringency between 0.015 and 0.049 and is then stretched in two stages, the first of which, for a birefringency B has a draw-ratio R determined by the equation:

%B+0.007 i ate" 0.07

the spun yarn being stretched at a total stretching ratio between 4.85 and 4.94.

The present invention relates to the application of polyamidic yarns to be used as tire reinforcements, namely the so-called Cord" yarns from nylon 6, obtainable by polymerization of caprolactam also called polycapronamide. As is known, cord yarns should have elevated tenacity with limited elongations. Owing to the thermoplasticity of polyamides the obtaining of said yarns with satisfactory properties appears not to be easy and has formed the object of numerous profound studies.

It has been known for a long time that it is possible and convenient for the attaining of elevated tenacities with low elongations to carry out the stretching of the yarns in a number of steps, in particular two steps. However, in carrying out that process, the stretching ratio utilized in the first stretching step acquires particular importance. According to what is described in the earlier art, in particular in British Patent No. 811,349, there is a relationship between the stretch utilizable in the first stretching step and the birefringency of the non-stretched extruded filaments and, in particular, the more elevated the birefringency, the lower has to be the ratio of the first stretching step. In said patent specification there is stated a formula relating these two variables and that is translated into a diagram giving with certain tolerances the stretching ratio of the first step adoptable with a yarn having a determined initial birefringency.

A subsequent British Patent No. 889,144 states that the limits put by Patent No. 811,349 are too narrow and ought to be widened and in particular they ought to be further widened if the yarn has been spun recently at the time at which it is subjected to stretching. This latter statement is easily understandable since freshly extruded yarn is in an unstable condition and has not yet developed its proper birefringency corresponding to the characteristic of the polymer and to the spinning conditions. A stable birefringency is attained in a period that may vary from some tens of minutes to some hours.

In said British patent specification No. 889,144 there is given a formula relating the stretching ratio of the first step with the birefringency of the yarn, whether for the case of normal yarn, that is to say, of yarn that was reeled after spinning and left at rest for a time sufficient to attain its stable birefringency, or for the case of freshly extruded yarn. However, though in said specification it is ice said that the extension of the limits fixed by the earlier British Patent No. 811,349 is applicable also to polycapronamide, there is no material example of stretching of polycapronamide given beyond the limits stated by the earlier one of the two patents.

In any case, following the disclosures of said patents, if one operates with a yarn having a birefringency (as determined by the method described by Heyn in Textile Research Journal 22, 513, 1952) comparatively high, for instance of the order of magnitude of 0.020-0.030, the ratio of the first stretching step must be kept comparatively low, which makes it impossible to obtain elevated tenacities in industrial scale. In the cited British specification No. 889,144 it is stated that by the process described therein yarns are obtained that can have a tenacity of at least 7 gr./den. and even a tenacity of up to 9.0 gr./den.

However it is not said what the conditions are for attaining said second more elevated limit of tenacity, in particular if one starts from polycapronamide which as is known presents greater difiiculties in working for the manufacture of cord, as compared with polyhexamethylene adipamide.

In the cited specifications an example is given of obtainment of a polycapronamide yarn that is said to have a tenacity of 9.5 gr./den., but in that case one starts from a yarn having a birefringency only of 0.006 in such a manner that one can give the first step of the stretching an elevated ratio, of 3.2. This makes it necessary, starting from a polymer of the kind dealt with in the example in question, that the coiling of the yarn should take place at a low speed, which evidently is extremely undesirable from the industrial point of view. It should also be noted that the obtaining of elevated tenacities is much easier to realize on an experimental scale, when the stretching is carried out under carefully controlled conditions, and it is much more difiicult to obtain on an industrial scale by a standardized and uniform process that does not involve excessive interruptions and difiiculties and does not re quire excessive attention of the operator continuously towards each stretching place.

It is an object of the present invention to provide a process for obtaining cord yarns starting from poly caprona-mides, and which permits obtaining regularly on industrial scale tenacities of more than 9 gr./den. while working with high spinning speeds and therefore, under very advantageous economical conditions.

According to the characteristic of the invention, the stretching, which is carried out as with the conventional technique in two steps, is made in such a way that in the first stretching step one gets a particularly elevated stretching ratio, which is at any rate more elevated than suggested by the prior art. 7

It should be noted that here there is made no particular reference to freshly spun yarn, but the invention applies to normally treated filaments, namely to filaments that have remained in the coiled state after extrusion and prior to being stretched for a sufiicient length of time to attain a stable birefringency. More in particular, according to the present invention, yarns .are stretched having a birefringency higher than 0.015 and preferably between 0.015 and 0.035 by spinning a polymer having an intrinsic viscosity not lower than 1.20 and normally of from 1. 20 to 1.50, the stretching speed being graduated in such a way as to get the desired birefringency starting from the polymer available, but at any rate keeping the spinning speed at least 350 m./1 minute and preferably at between 400 and 800 m./l minute, and carrying out the stretching in two steps in which the first step of stretching is carried out at a ratio determined in the following way: for a yarn having birefringency 0.015 the ratio of the first stretching step is substantially of from 3.5 to 4.

wherein B is the birefringency and R the draw-ratio at the first step of stretching. The following table indicates the maximum and the minimum draw-ratio for a number of birefringency values over 0.015, as calculated from the above equation (approximate at $0.01):

Draw-ratio Birclringency Max. Min.

0. 020 3. 72 3. 1G 0. 025 3. 60 2. S8 0. 030 3. 53 2. (i7 0. 035 3. 50 2. 50

From the graph of FIG. 1 and the above table it will be evident that the curves which define the hatched area of values flatten rightward, i.e. the profitable values tend to a constant for highest birefringency values. Therefore, it will be evident that as polymers having a birefringency above 0.035 not exceeding the maximum value of 0.050 are available for processing, such polymers can be drawn at a draw-ratio within the range stated for said latter birefringency.

It will be further evident that the profitable ranges widen as the value of birefringency increases, so that the findings of the invention may enjoy a greater latitude of actual working thereof as relatively high birefringency polymers are selected for practising the invention.

It will be further evident that, as said curves are relatively fiat and the ranges of profitable values of draw-ratio are pretty ample, acceptable draw-ratios can be readily found for polymers having a birefringency intermediate between 0.015 and 0.035, simply by linearly interpolating the values indicated for lower and upper birefringencies.

According to the invention it is possible to spin yarns having viscosity higher than 1.50 and birefringency higher than 0.035; and this in particular is possible if one employs for extrusion drawing apparatus a melting member to which the solid polyer is fed by gravity and from which the molten polymer flows down, again by gravity.

In that case, the ratio of the first stretching step remains between the fixed limits valid for the birefringency of 0.035 namely between 2.5 and 3.5.

The invention will be more fully clear from some working examples described with reference to FIGURES 2 and 3 which diagrammatically represent two different stretching devices, but the stretching may be carried out with any known stretching device, according to what appears to be more convenient in the individual cases.

Preferably, in embodying the present invention, stretching devices are employed wherewith the stretching takes place in two steps between two groups of rolls driven at different peripheral speeds without or with the intermediary of a stretching pin, which is heated or not.

Consequently, with both embodiments, as represented in FIGURES 2 and 3, the yarn coming from a coiling device not represented in the figure, is stretched in a first step between two systems of rolls 11 and 12 and in a second step between the two systems of rolls 12 and 13 to be then coiled upon a spindle or cop 14 with ring 15. The numeral 16 indicates a thread-guide and the numeral 17 a cylinder that controls the rotation of the roll 11. The numeral 18 indicates another thread-guide interposed between the system 13 and the ring 15.

Now with reference to FIGURE 2, the roll 19 of the group of rolls 12 of the first stretching step, which draws and stretches the thread and has, therefore, as compared with the roll 11, a higher peripheral speed, has its surface heated to a temperature between C. and 200 C. and preferably between C. and C., while in the case of FIGURE 3 roll 19 is not heated, but between the groups of rolls 12 and 13 of this figure there is interposed a heating device 20 to be heated to temperatures between 150 C. and 200 C. and preferably between 170 C. and 185 C.

As already said before, in the path of the thread between the rolls 11 and 19 on one hand and 19 and 21 on the other hand, there can be inserted stretching pins held at room temperature, or heated to temperatures of from 40 C. to 75 C. and preferably to temperatures of about 60 C.

The peripheral speeds of the rolls 19 are between 80 and 400 m./l minute and preferably between 150 and 300 m./min. for the device according to FIGURE 2, and between 90 and 175 m./min. for the device represented by FIGURE 3.

Example 1 A sample of polycapronamide having intrinsic viscosity 1.32 (viscosity determined in solution of m-cresol at concentration of 0.5 gr./dl. and calculated according to Carother by means of the formula s 2.3 log t: C

was spun with count of 3700 denier at 136 filaments and collected at a speed of 400 m./1 min. The yarn obtained has a birefringency (stable also after some days) according to Heys method (Text. Research Journal 22, 513', 1952) of 0.025. Said yarn was stretched in two steps on a stretching machine (of the kind of that of FIGURE 2) wherein the first stretching step was adjusted to a ratio of 3.27 and the second stretching step was adjusted in such a way as to get a total stretching ratio equal to 4.94 (collecting speed of the yarn spin 350 m./1 minute). The yarn obtained had the following average dynamometric characteristics:

Tenacity gr./den 9.6 Elongation percent 16 Initial modulus gr./den 38 The stretching process took place regularly without any inconvenience.

Example 2 A sample of polycapronamide having intrinsic viscosity 1.41 (determined and calculated as described in Example 1) was spun at 6300 denier at 204 filaments and collected at a speed of 600 m./1 minute. The yarn obtained has a final 'birefringency (stable) of 0.031. Said yarn was stretched in two steps on 'a machine (of the type accord- 'ing to FIGURE 3) wherein the first stretching step was adjusted at a ratio of 3.20 and the second step was adjusted in such a way as to obtain an overall stretching of 4.85. Speed of collecting the yarn spun: m./1 minute (peripheral speed of the roll 19:126 m./1 minute. The yarn obtained had the following average dynamometric characteristics Tenacity gr./den 9.5

Elongation percent 15.5

Initial modulus gr./den 37 Example 3 A sample of polycapronamide having intrinsic viscosity 1.35 (viscosity determined and calculated as described in Example 1) was spun with count 3700 denier at 136 filaments and collected at a speed of 750 m./1 minute. The yarn obtained has a b irefringency of 0.037. Said yarn was stretched in two steps on a stretching machine of the type according to FIGURE 2 with rod at 60 C. between the first and second roll, in which the first step of stretching was adjusted to a ratio of 3.13 and the second step was adjusted in such a way as to get a total stretching ratio equal to 4.85 (collecting speed of the stretched yarn 350 m./min.). The yarn obtained had the following average dyn amometric characteristics:

Tenacity gr./-den 9.6 Elongation percent 14 Initial modulus -gr./den 36 The stretching process took place regularly without any inconvenience.

Example 4 A sample of polycapronamide having intrinsic viscosity 1.25 (determined and calculated as described in Example 1) was spun at 6300 denier at 2.04 filaments and collected at a speed of 380 m./1 min. The yarn obtained has a birefringency of 0.018. Said yarn was stretched in two steps on a machine of the type according to FIGURE 2 in which the first stretching step was adjusted to a ratio of 3.48 and the second step was adjusted in such a way as to obtain a total stretching of 4.94 (speed of collecting the yarn spun=180 m./1 minute).

The yarn obtained had the following average dynamometric characteristics:

Tenacity gr./den 9.5

Elongation percent 14.5

Initial modulus gr./den 40 Example 5 A sample of polycapronamide having intrinsic viscosity 1.48 (determined and calculated as described in Example 1) was spun at 3700 denier and at 136 filaments and was collected at a speed of 7 00 m./min. The yarn obtained shows a final birefringency of 0.049. Said yarn was drawn in two steps on a machine of the type shown in FIG. 2, in which the first drawing step was adjusted to a ratio of 2.99 and the second step was adjusted in such a way as to obtain a total drawing ratio of 4.85, at a winding speed for the drawn yarn of 180 m./min.

The yarn obtained had the following average mechanical characteristics:

Tenacity gr./den 9.5 Elongation percent Initial modulus gr./den 38 The embodiments of the invention in which an exclusive property or privilege is claimed are defined \as follows:

1. A process for producing polycapronamide cord yarns having a tenacity of at least 9 gr./den. and elongations not greater than 18%, comprising spinning polycapronamide having an intrinsic viscosity from 1.25 to 1.48 at a spinning speed between 380 and 750 m./minute, obtaining a spun polycapronamide having a birefringency between 0.018 and 0.049, subjecting the spun polycapronamide to a first stretching step at a draw-ratio R determined by the equation:

wherein B indicates the birefringency of the spun yarn, and successively subjecting said spun and drawn yarn to a further stretching step to stretch said spun yarn finally at a total stretching ratio between 4.85 and 4.94.

2. The process of claim 1, wherein a polycapronamide having an intrinsic viscosity between 1.25 and 1.32 is spun at a speed between 380 and 400 m./minute to produce a spun yarn having a birefringency between 0.018 and 0.025, and is subjected to a first stretching step at a draw-ratio between 3.27 and 3.48.

3. The process of claim 1, wherein a polycapronamide having an intrinsic viscosity between 1.35 and 1.48 is spun at a speed between 350 and 800 m./minute and having spun yarn having a birefringency between 0.031 and 0.049 and is subjected to a first stretching step at a draw-ratio between 2.99 and 3.2.

4. The processing of polycapronamide filamentary material having elongation not greater than 18%, and spun at a speed between 350 and 800 m./rninute and having a birefringency between 0.015 and 0.049, comprising the steps of subjecting said material to a first stretching operation at a draw-ratio R within the limits defined by the equation:

1/3B 0.07 as a function of its birefringency B, and further stretching said material to stretch said material finally at a total stretching ratio betwen 4.85 and 4.94, to provide polycapronarnide cor-d yarns having a tenacity of at least 9.5 gr./den.

5. In the process of claim 4, providing filamentary material by spinning polycapronamide having a viscosity between 1.20 and 1.50.

6. In the process of claim 1, subjecting spun filamentary material having a birefringency of about 0.015 to a first stretching step at a draw-ratio in the range of 3.5 to 4.

7. In the process of claim 4, subjecting spun filamentary material having a birefringency of about 0.035 to a first stretching step at a draw-ratio in the range of 2.5 to 3.5.

8. In the manufacture of high tenacity cor-d yarns of polycapronamide polymer, spinning polycapronamide having a viscosity and at a spinning speed such to provide filamentary material having a birefringency over 0.015, and subjecting said material to two-step stretching wherein the first step comprises subjecting a material having birefringency between 0.015 and 0.035 at a mean drawratio between 3.5 and 4, and between 2.5 and 3.5 respectively.

9. In the manufacture defined in claim 8, subjecting filamentary polycapronamide material having a birefringency B of between 0.015 and 0.035 to 'a first stretching step at a mean draw-ratio R calculated as within the limits of References Cited UNITED STATES PATENTS 3,016,684 1/ 1962 Less ig 2872 3,091,015 5/ 1963 Zimmerman. 3,311,691 3/1967 Good 264290 FOREIGN PATENTS 811,349 4/ 1959 Great Britain.

JAMES A. SEIDLECK, Primary Examiner.

T. MORRIS, Assistant Examiner. 

